There are various control methods for adjusting an output voltage, i.e. an alternating-current (AC) voltage, of an inverter to a rotary electric machine to control the rotary electric machine accordingly. The various control routines include, as two typical control routines, a pulse-width modulation (PWM) control routine and a torque-feedback control routine; the PWM control routine is a type of current-feedback control routines.
The PWM control routine sets a sinusoidal base voltage as a voltage command for the output voltage of an inverter based on both a command value for output torque of a rotary electric machine and output currents output from the inverter to the rotary electric machine. Next, the PWM control routine compares the sinusoidal base voltage with a carrier wave having a higher frequency than the frequency of the sinusoidal base voltage. Then, the PWM control routine controls, based on the comparison results, the inverter to adjust the output voltage of the inverter accordingly.
The torque-feedback control routine obtains measured values of output currents, each of which has a predetermined phase, to a rotary electric machine. Then, the torque-feedback control routine calculates an estimated value of output torque of the rotary electric machine according to the measured values of the output currents. The torque-feedback control routine compares the estimated value of the output torque with a command value for the output torque of the rotary electric machine. The torque-feedback control routine adjusts, based on the comparison results, the pattern of a pulse output voltage to be output to the rotary electric machine.
The PWM control routine has an advantageous effect of reducing fluctuations of the output torque in a low rotational speed of the rotary electric machine, but may limit the voltage utilization factor of the inverter. The torque-feedback control routine has a higher inverter voltage utilization factor, but may have more fluctuated output torque of the rotary electric machine in a low rotational speed range thereof. In view of these circumstances, some control apparatuses are configured to selectively use the PWM control routine and the torque-feedback control routine to control a rotary electric machine, one example of which is disclosed in Japanese Patent Publication No. 5368777.